DS was a McDs everyday baby, cause where I worked it was the safest easy to reach food for lunch! only gained 7kg on that regime
DD was alot healthier and less food in general, mainly cause my stomach always felt so full of baby there wasnt room for food and gained 12 kg.
I was walking with DS to help with the morning sickness (which it did) and couldn't with DD as I'm sure I was huge from the day one! so my advice is the exercise may help both sickness and weight.